1. Technical Field
The present invention relates to a technique for reducing an optical path length in an optical system for performing reading or recording of information by making use of light irradiation onto an optical recording medium.
2. Description of Related Art
An optical head apparatus (such as an optical pickup apparatus) to be used for the reproduction and recording of information associated with an optical disk is provided with, for example, a light source such as a laser diode, lens elements (such as a collimator lens and a coupling lens) which convert light scattered from the light source into an approximately parallel light beam, and an objective lens which condenses the light beam onto a disk recording surface to its diffraction limit. Light irradiated on to the disk from the objective lens and modulated by the disk is converted to an electrical signal in a light-receiving part using a photodiode, whereby reading of information is performed. For example, as an optical integrated construction, a form in which a laser emission part and a light-receiving part are integrally formed is enumerated (refer to, for example, Patent Document 1: Japanese Patent Application Publication No. Hei10-222859.)
In a pickup apparatus having an optical system in which this integrated element and lens elements are combined and arranged so that the necessary mutual distance is maintained between the elements, a mirror for changing an optical path is disposed on an optical path for the purpose of reducing the entire thickness. In this case, the pickup apparatus needs to have a certain extent of size (an area as viewed from the optical-axis direction of irradiation onto the disk), and the addition of the mirror increases the number of optical component parts and causes a cost increase.
If the apparatus size is to be made small and the number of component parts is to be reduced, it is preferable to avoid as much as possible the use of an optical-path-changing element. Namely, as a form of optical arrangement, it is desirable that light exiting from a laser emission point to be irradiated onto a disk after having traveled rectilinearly without undergoing much optical-path change and been transmitted through lens elements and an objective lens, and that return light from the disk also travels rectilinearly and reaches a light-receiving part.